This invention relates to a universal joint and more particularly a tripot universal joint.
Tripot universal joints are typically employed in automotive axial driveshafts and especially in front-wheel-drive vehicles between the transaxial differential and the driving wheel. The telescopic constant velocity joint such as the tripot should not only transmit the torque at various speeds, angles and telescopic positions but also prevent any vibrations of the engine from being transmitted through the joint and driveshaft to the driving wheel and the vehicle structure. In addition, when the universal joint operates at an angle it should not produce any osculating axial excitation which may be capable of initiating vibrations in the driveshaft or in the structure of the vehicle.
U.S. Pat. No. 3,125,870 granted to Michael Orain, Mar. 24, 1964, discloses a conventional telescopic type tripot universal joint of the prior art, which is one of the best stroking type universal joints available for osculating engine vibrations from the rest of the vehicle. However, these conventional prior art tripot universal joints due to their operating friction characteristics produce internally generated osculating axial forces which are related to the transmitted torque angles. During severe accelerations at low vehicle speeds these cyclic axial forces can be of sufficient magnitude to produce a shudder type disturbance which has a frequency equal to three times the shaft speed.
To reduce this shudder or vehicle ride disturbance, the generated axial forces must be reduced. This reduction is accomplished by tracking an outer ball or ball assembly of the tripot universal joint relative an axis of the housing. Effective tracking of the outer ball to reduce shudder must have a housing ball bore or channel designed to minimize the outer or ball assembly tip and/or reduce binding of the ball within the track when it does tip. However, ball tip occurs about two different axes, the X-axis and Y-axis. The problem with previous designs is the effectiveness at preventing ball pivoting about the Y-axis. The inability to prevent ball tip results in increased generated axial forces which lead to shudder.
A telescopic universal joint comprises a first drive member having a first longitudinal axis engaged flexibly to a second drive member having a second longitudinal axis. The first and second longitudinal axis are co-linear to one another, or zero degreed, when the joint is not flexed. The first drive member defining three longitudinal drive channels spaced circumferentially from another. Each channel has two opposing concave side surfaces spaced circumferentially apart by a back surface facing radially inward. Three trunnions of the second drive member are disposed respectively within the three channels. Each trunnion has a radial axis all lying within an imaginary plane and intersecting at a spider center lying along the second longitudinal axis.
Rotating and wobbling about each trunnion is a ball assembly having an outer ball which is in rolling contact with one of the two opposing concave side surfaces of the first member. Each side surface has a lateral cross section profile which is substantially parabolic in shape wherein a radius of curvature becomes smaller as the profile extends radially outward with respect to the first drive member.
Preferably, an outward portion of the side surface is formed contiguously between the back surface and an inward portion of the side surface. The lateral cross section profiles of the inward and outward portions forming the parabolic profile of the side surface. The radius of the outward portion profile is smaller than a radius of the inward portion profile, and the radius of the inward portion profile is larger than a maximum radius of the outer ball extending from a center point of the ball assembly to a tread face of the outer ball which directly opposes the side surfaces of the channel.
An advantage of the present invention is the reduction of outer ball binding with the channel by eliminating contact between the tread face of the outer ball and the inward portion of the unloaded side surface of the channel regardless of joint flexing.
Yet another advantage of the present invention is the reduction of universal joint studder.